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CHRISTINE ROMANS, CNN ANCHOR: Breaking news this morning. The underwater search for missing Malaysia Airlines Flight 370 intensifies. Just over an hour ago, investigators reveal what the Bluefin submarine saw its first day combing the bottom of the ocean, this as we learn the details about what was happening in that plane's cockpit just before it disappeared.

Was the co-pilot trying to send someone a warning?

We're live with the very latest this morning.

VICTOR BLACKWELL, CNN ANCHOR: Also, a tense standoff in Ukraine. Pro-Russian protesters refuse to disarm, refuse to step aside. They're ignoring Ukraine's threat to send in troops, as the U.S. and Russia blame each other for the intensifying crisis.

Is war imminent?

We're live with what's happening right now.

Good morning. Welcome to EARLY START. I'm Victor Blackwell.

ROMANS: I'm Christine Romans.

Nice to see you again today, Victor.

BLACKWELL: Good to be here.

ROMANS: It's Tuesday, April 15th, 4:00 a.m. in the East.

We begin with the latest in the search for Malaysia Airlines Flight 370 and the news breaking overnight that an unmanned underwater vehicle, this Bluefin-21, found nothing of interest during its first search of the floor of the Indian Ocean. That journey ended abruptly after just six hours, when the unmanned sub had to surface after going too deep.

This morning, crews preparing again to put the vehicle back in the water for another 16-hour trip, they hope, scanning for wreckage from that jet, missing now 39 days.

Erin McLaughlin is live in Perth with the latest on the search.

Erin, they reached the maximum depth this submersible could go.

ERIN MCLAUGHLIN, CNN CORRESPONDENT: That's right, Christine. It's also important to note that it had only been searching the ocean floor for about two hours in total. It takes it about two hours to get down and then two hours to get back up. So, two hours in total. It's supposed to search for some 14 more, perhaps not surprising that it didn't find anything. Now, it has been some 17 hours since it resurfaced, and they still have yet to put it back into the water due to poor weather conditions.

Now, officials here in Australia have long said that this is going to be most likely a slow and painstaking process. Day one of this phase of the operation, that certainly seems to be the case.

Now, in terms of what happened when the Bluefin-21 was down there, it was on the utter edges of the search field when it encountered very deep waters, deeper than the 2.8 miles or so that is at its capacity, so it re-emerged on to the surface to be reprogrammed. We understand that officials are currently adjusting the search area to account for those deep waters so that it doesn't go over its capacity -- Christine.

BLACKWELL: Meanwhile, we're learning new details about what was going on inside the cockpit of that 777. A U.S. official tells CNN the co- pilot's cell phone was turned on during the flight and tried to make contact with the cell phone tower over Penang.

Well, that attempt was roughly 30 minutes after the plane made that aggressive left turn off course.

Senior international correspondent Nic Robertson is live in Kuala Lumpur with the latest on the investigation.

So, Nic, we've got this new information. What's the significance?

NIC ROBERTSON, CNN SENIOR INTERNATIONAL CORRESPONDENT: Well, the significance shows that the plane appears to have been at a relatively low altitude as it passed across the coastline from the Malaysian peninsula out into the sea. We're told that once it got about 18 miles out into the sea, it actually got to around about 4,000 to 5,000 feet above sea level, dipped quite low before it reappeared again on the radar.

So, this does indicate that the aircraft, as it came over the Malaysian peninsula, was not, or possibly not at cruising altitude for this connection to be made between a cell phone and a cell tower, not a full conversation itself, not a call made, but just a data connection, a handshake with the cell tower.

We've also heard from the acting transport minister today, talking about what will happen when that black box is discovered and potentially recovered from Flight 370. He said that part of it will -- part of the decision about its future will be done in consultation with the International Civil Aviation Organization, but a lot to be discussed about it. This is what he said.

(BEGIN VIDEO CLIP)

HISHAMMUDDIN HUSSEIN, MALAYSIAN ACTING TRANSPORT MINISTER: Whether it is an ICAO practice, whether it is a challenge which involves diplomacy, because you must understand that it involves 14 nations. And when it comes to the search and rescue, at the beginning, it involves 26 nations.

So, we have diplomatic challenges, we've got legal challenges, we've got next of kin, and that is why we have established these committees.

(END VIDEO CLIP)

ROBERTSON: And that's what they're working through right now, but he did go on to say that all the data from the black box, if and when it would be recovered, he said there will be full truth from this and a full accounting of it -- Victor.

ROMANS: And now to Ukraine, a country on the brink of civil war. Pro-Russian militants this morning continue to hold government buildings in the eastern part of Ukraine, despite calls for them to give up their arms and leave. They are not budging. At least they don't appear to be budging.

President Obama and Vladimir Putin spoke last night, trading barbs over who is behind the escalating violence, as Ukraine's acting president is asking the U.N. to send in peacekeepers.

Phil Black live for us in Kharkiv, Ukraine, with the very latest.

Fill us in here. I mean, every day, it seems like a slight escalation in these tensions.

PHIL BLACK, CNN CORRESPONDENT: That's right, Christine, and what it means, what the trend is, is that the authority of the central government in Kiev is slipping away, and that Ukrainian government so far has appeared to be powerless to reverse that trend.

In nine separate towns and cities across the east here, pro-Russian protesters and militants have stormed key government buildings. They now occupy those and key pieces of infrastructure, and the government in Kiev has not been able to do or say anything that seems capable of dislodging them from those locations. It has tried talk of threats, force, ultimatums, deadlines, the ongoing talk of a large-scale anti- terror operation, but we've seen no sign of it.

They've also tried to be more conciliatory, with talk of amnesties, and negotiations and political conclusiveness in determining the future political structure of this country. But again, no impact. Now, there is this suggestion from the Ukrainian government for an international peacekeeping force here operating under a United Nations mandate. That was the suggestion made by the acting Ukrainian president to the U.N. Secretary-General Ban Ki-moon, and it is, perhaps, a sign of just how desperate the Ukrainian government is. We can only guess the appetite that exists in Western governments to see their soldiers here on the ground staring down against Russian forces across the border.

But the other key point is that a force like this would almost certainly need at approval of the United Nations Security Council, and Russia has, as a permanent member, a veto on the Security Council. It is very difficult to imagine a scenario where Russia would allow western soldiers to be here in eastern Ukraine, so close to its border.

So, at the outset, that idea also appears to be a nonstarter, Christine.

ROMANS: Meantime, the tensions just keep moving higher and higher. All right, Phil Black. Thank you so much, Phil.

Happening right now, an Olympic hero returns to the witness stand after breaking down in front of a packed courtroom while he was trying to explain why he shot and killed his model girlfriend. We are live with what Oscar Pistorius is saying this morning.

BLACKWELL: And Boston strong one year later, marking the first anniversary of the marathon bombings. What the city is planning today. That's next.

(COMMERCIAL BREAK)

BLACKWELL: Ten minutes after the hour now.

Oscar Pistorius is back on the witness stand again this morning at his murder trial, and seemingly, he's holding his own against this intense cross examination. The prosecutor is trying to catch Pistorius in lies over what happened the night he shot and killed his girlfriend, Reeva Steenkamp. Testimony just resumed a few moments ago.

CNN legal analyst Kelly Phelps is at the courthouse in Pretoria. Kelly, Pistorius has spent more time on the stand than any other witness in this trial. This, though, is going to wrap up pretty soon, right?

KELLY PHELPS, CNN LEGAL ANALYST: Yes. We expect -- we heard this morning, Mr. Nel asked for a postponement, essentially, after Pistorius has concluded his testimony, and he indicated that he should be finished with cross examination today. And then all that's left after that with regards to Mr. Pistorius' testimony is the opportunity for his legal counsel to re-examine him, which should be significantly shorter than cross examination.

BLACKWELL: The prosecutor also asked for a two-week postponement, a two-week recess, I guess. Tell us about that.

PHELPS: Well, really, it appears to be more practical and personal reasons. In South Africa, we have a spate of public holidays coming up, so over that two-week period, there would really only be a few active court days.

And Nel, with the agreement of Barry Roux, has requested that the trial should be put on hold over those two weeks so that they can, first of all, deal with other matters, other cases that they're working on, and also, essentially, take some personal time off.

BLACKWELL: Kelly, there is a point at which the prosecutor made a statement and then Pistorius corrected him. The prosecutor used that opportunity to say that Pistorius is a stickler for detail.

Was that seen as maybe a snipe, showing some personal animosity, or is that something we should expect in this type of cross examination?

PHELPS: Well, I think it's a classic characteristic of Nel's cross examining style. He is known to be quite acerbic and cutting and sarcastic, and it is part of, in a sense, the mental game that he plays with the person that he's cross examining, to try and get under their skin, catch them off guard, with the hopes of essentially catching the person out in telling an inconsistency or a mistruth along the way.

So, it's quite classic in terms of Mr. Nel's style in the courtroom.

BLACKWELL: Does this length of the cross examination going now into week two, although expected to wrap up at the end of the day, according to the prosecutor? Is it seen as belaboring the point, or is Nel poking significant holes into Pistorius' story?

PHELPS: It's certainly not seen as belaboring the point, and we know that from the judge's own participation in the trial yesterday. So, Mr. Roux yesterday actually asked if Mr. Nel could be asked to move on from the subject matter he was questioning around, and the judge herself said, no, I do not believe he is covering same ground over and over ingenuously, but that he is still trying to get to the bottom of the story and inconsistencies, and it therefore plays a very valid role in the court's truth-finding process.

However, should he get to the point where the judge feels he is gratuitously retreading ground simply to wear Pistorius down, she would have absolutely no hesitation to intervene at that stage. But right now, he's tread that line very closely, but he has stayed on the right side of it.

BLACKWELL: And could possibly, as you had indicated, wrap up today.

Kelly Phelps in Pretoria for us -- Kelly, thank you.

ROMANS: A solemn anniversary today in Boston. One year -- one year since a bombing destroyed the calm of the Boston marathon, shattering hundreds of lives, leaving three dead and more than 260 injured.

Today, that city focused on remembering the fallen and also looking forward to a memorial ceremony this afternoon that's going to pay tribute, and there will be a moment of silence to mark the time the first bomb went off. But "Boston strong" banners hang everywhere, and the marathon will go on as scheduled next week. Many of those running say they're doing it in honor of those who now can't run the course themselves, and they want the world to know that city cannot be knocked down.

BLACKWELL: We could find out today if a man police say shot and killed three people at a Jewish center and retirement community near Kansas City will face state and federal hate crime charges. Frazier Glenn Cross, also known as Frazier Glenn Miller, is in jail, and federal prosecutors say they have enough evidence to bring hate crime charges in federal court, and that means he could face the death penalty.

Cross is a former grand dragon of the Ku Klux Klan and had a history of racist and anti-Semitic rhetoric. The three people he's accused of killing are Christians.

Now, Dr. William Corporon and his grandson, Reat Underwood, they were at the center for a singing competition. Terri LaManno was killed outside of a retirement community where her family says she'd gone to visit her mother. And today would have been her 25th wedding anniversary.

ROMANS: California police say a pair of sex offenders charged now with raping and killing four women were wearing court-ordered GPS devices during those crimes. The two are suspected of a string of attacks beginning last fall, and police say they are confident there's a fifth victim. Both men had been ordered to wear the devices after serving prison terms for sexually assaulting a child under the age of 14.

BLACKWELL: A second mental health evaluation will move ahead in the Colorado movie theater shooting case. A judge is turning aside attempts by defense lawyers for James Holmes to block the examination. The judge threw out an earlier exam. He said it was inadequate. Holmes has entered an insanity plea for the July 2012 shooting, 12 people were killed, 70 others were injured.

ROMANS: Police this morning say a Utah mom suspected of killing six of her newborn babies has admitted to the killings. Thirty-nine-year- old Megan Huntsman reportedly told police she strangled or smothered the infants immediately after they were born. Seven tiny corpses were found Saturday in a garage at Huntsman's former home, one thought to be stillborn. She's being held on six counts of murder. No word yet on her motive.

BLACKWELL: Happening today near Pittsburgh, students are being allowed to visit Franklin regional high school, the site of a stabbing and slashing attack that left nearly two dozen people hurt, some critically. The counselors and a few therapy dogs will be at the school just one day before classes officially resume. The suspect in the attack, Alex Hribal, is being held without bail. He faced attempted murder and assault charges.

ROMANS: New details this morning about the bus crash on a northern California interstate that left 10 people dead, many of them high school students. Officials say the driver of the bus and the FedEx truck that crashed into it both had clean driving records.

This morning, one of the students on board is being called a hero. Officials at his high school say Ismail Jimenez (ph) died trying to help others escape the bus. The students on board were from southern California. They were heading north for a college tour.

BLACKWELL: The woman caught on camera throwing a shoe at Hillary Clinton during a speech in Las Vegas -- you've seen this video -- well, the woman is now in federal -- she's facing federal charges, rather. Police have identified the woman as Alison Michelle Ernst from Phoenix, but authorities are not saying why she potentially threw the shoe at the former secretary of state. New charges include trespassing and violence against a person in a restricted building, on top of misdemeanor disorderly conduct charges from Las Vegas police.

ROMANS: All right, Obamacare may not drive up health care costs as much as previously thought. New estimates from the Congressional Budget Office and the Joint Committee on Taxation, these new estimates show premiums are only likely to rise about 3 percent in 2015, far less than many had been predicting, and the overall cost for implementing the law expected to run about $5 billion less than expected, but less money in penalties will be collected because the administration decided to delay the employer coverage mandate.

BLACKWELL: Extreme weather ripping through the south overnight. Look at this. This is from Mississippi.

ROMANS: Oh, my!

BLACKWELL: Not far from Biloxi.

Officials say that heavy winds damaged dozens of trailers here at this RV park, some of them, as you see here, flipped over. Unfortunately, at least two people have been hurt.

ROMANS: That storm system is now moving east. Indra Petersons' tracking all this weather for us.

Hey, Indra.

INDRA PETERSONS, AMS METEOROLOGIST: Good morning.

What an unbelievable morning. We're talking warm conditions and some rain on the East Coast, but notice right behind it, right in Cincinnati, we are talking about snow.

Look at this! You're talking about temperatures ahead of the cold front into the 60s. Right behind it, we're talking about the snow, 30s and even 20s.

So, yes, the cold air is expected to make its way in, and eventually, that rain will turn to snow, just a couple of flurries into the overnight hours into the Northeast.

Look at the explosive nature, though. So, down into the Southeast, you can almost see these storms blowing up. That's all thanks to the instability that's been out there. We've had, of course, some of the convective weather, so yes, still a slight risk today. It has shifted farther to the east, though, so from Norfolk, all down through Florida, even places like Jacksonville, we're still talking about the threat for severe thunderstorms and strong straight-line winds.

That's really been the story here. Notice, we're still talking about the winds ahead of the cold front, bringing in the warm air, but behind it, it's going to shift. We're going to talk about the cold air making its way into Canada and that's going to transition that rain back over to snow. You can actually see the line of storms again today progressing, moving the rain into the Northeast, right around commute time, lasting throughout the day, into the overnight hours.

And on the back side of it, we're actually going to be talking about flurries. Let's talk about what we're expecting. Heavy rain, even about two inches up towards New York City, then some snow. Just, again, a little bit in the overnight hours.

Hard to believe, but the temperature drop will be even the most painful thing because it's been so nice. Now I feel like we're already used to it, but no, long gone.

ROMANS: Let's talk about the moon instead. Please?

BLACKWELL: Yes, can we talk about that?

ROMANS: Please, no snow flurries.

PETERSONS: It was gorgeous. Did you have a chance to see it?

ROMANS: It was too foggy.

BLACKWELL: I walked out and just saw more buildings.

PETERSONS: I was going to say.

ROMANS: There it is. These are stunning pictures to show you now of the spectacular sight in the skies. Just happened less than an hour ago, a lunar eclipse turning the moon blood red, something scientists say is pretty rare. It's all because of the way the earth block light from reaching the moon. Rather than blocking it out, the light was bent in the earth's atmosphere and reflected back, and that's the result.

This is the first of four lunar eclipses expected in the next two years, this series of lunar eclipses. I know some people who are trying to get their kids to see all of them, right?

BLACKWELL: Yes.

ROMANS: This is the first one. They've knocked this off the list. I couldn't see it. Too foggy, too much cloud cover.

BLACKWELL: Live picture here, and it's beautiful with that purpose hue on one edge there. It's beautiful. Wish I could have seen it, but this is good, too. This is good. ROMANS: All these folks stayed -- they stayed up in L.A. on the West Coast so they could see it, and lots of discussion on social media about how beautiful it was.

ROMANS: All right, happening now, searching the sea bed for missing Malaysia Airlines Flight 370. A submarine set to deploy again miles below the surface.

What do we really know about the deepest depths of this ocean? We've got an expert to explain just how uncharted this terrain is.

(COMMERCIAL BREAK)

BLACKWELL: We're following the latest breaking news this morning in the search for Flight 370, now missing for 39 days. Authorities say an unmanned underwater vehicle turned up nothing of interest during its first day scanning the ocean floor. The Bluefin-21 is set to return to the water this morning for a 16-hour mission, just a day after its first mission had to be cut short because it descended too deep.

ROMANS: What makes the search even more difficult is the fact this part of the ocean has barely seen human eyes, been seen by human eyes. And oceanographers say they have no idea what it really looks like so far below the water's surface.

(BEGIN VIDEO CLIP)

SYLVIA EARLE, OCEANOGRAPHER: Only about 5 percent of the ocean has been mapped with the same degree of accuracy that we have for the moon or Mars or even Jupiter. And the southern Indian Ocean is -- it's one of the least explored, least known parts of the planet. Some people think that Earth is well-explored.

Actually, the greatest era of exploration is just beginning, because we're just beginning to have the right equipment to be able to explore the deep part of the ocean, and most of the ocean, as they say, it is the average depth 2 1/2 miles, and this aircraft is thought to be in water a bit deeper than that.

And just imagine being in an airplane three, two, 2 1/2 or three miles up in the sky and then trying to operate at a point on the land below. This is what these ships basically are challenged with, trying to imagine what is three miles below when you can't see what is there. So, this is very exciting, tricky, challenging business.

We have technology that can take us to the moon, but we still have trouble getting to the deep sea.

(END VIDEO CLIP)

ROMANS: And they'll be learning so much about that ocean floor in the Indian Ocean there in the process of trying to find that jetliner.

A lot happening this morning in the search for the vanished jet. As we learn new details about what's happening in the plane's cockpit before it disappeared. You don't want to miss that.